1. Field of the Invention
The present invention pertains to a process for manufacturing multiple quantum-well (MQW) lasers for use in fiber optic communications systems. More particularly, the present invention relates to a process for controlling target lasing frequencies of MQW lasers.
2. Description of Related Art
MQW lasers are widely used in fiber optic communication systems to launch carrier wavelengths (.lambda.) along an optic fiber. The carrier wavelengths are modulated by data signals and transmitted along fibers in the system. Typical "standard" carrier wavelengths at which components of fiber optic systems, such as receivers, couplers, routers, etc., are designed to operate are 1.3, 1.4 and 1.5 .mu.m. Thus, lasers used in existing systems are specifically designed to produce a lasing wavelength at a particular one of these target wavelengths.
A common method of producing MQW lasers utilizes metal-organic chemical vapor deposition (MOCVD) reactors wherein lasers are epitaxially grown on sulfur-doped InP (S-InP) wafers or substrates. The S-INP substrates are typically bulk-produced to yield wafers having doping concentrations within a range of 3 to 6.times.10.sup.18 /cm.sup.3. The bulk-produced substrates are then used to mass produce In.sub.1-x Ga.sub.x As.sub.y P.sub.1-y MQW lasers in batches by setting MOCVD reactor parameters, e.g., temperature, pressure, duration and concentration of deposition dopants, etc., in an attempt to yield batches of lasers which produce a desired target wavelength (.lambda.), e.g. 1.3 .mu.m lasers.
Prior to batch production, a test run is typically performed in each reactor by placing one or more substrates in a common reactor and adjusting the reactor parameters to yield the desired lasing wavelength (e.g. 1.3, 1.4 or 1.5 .mu.m). Lasers within an acceptable range, e.g. .+-.7 nm of the target wavelength, are usable whereas lasers outside of this range are discarded. If a test run is successful, then a batch run is conducted and the resulting lasers are tested to determine whether they are in fact within the desired range of the target wavelength.
A problem with known laser batch production techniques is that the batch production yield is oftentimes unacceptable because numerous lasers from each batch generate lasing wavelengths outside of the acceptable range of a target wavelength. This results in the discarding of numerous lasers and, consequently, an increase in laser production costs.